PROJECT SUMMARY & ABSTRACT This K01 Career Development Award addresses the significance of three key modifiable behaviors (physical activity, energy intake, and sleep) for weight loss and weight loss maintenance. Previous investigations have identified that the absolute amounts of physical activity (200-300 min/wk) and energy intake (~1800 kcal/day) are associated with weight loss and weight loss maintenance. In addition to physical activity and energy intake, epidemiological and controlled laboratory studies suggest that sleep is important for bodyweight regulation; however, the importance of sleep during a behavioral weight loss intervention has not yet been evaluated. This study will be one of the first studies to evaluate if indices of sleep are associated with enhanced adherence to physical activity and energy intake prescriptions during a weight loss intervention and greater weight loss. Findings from this study may lead to more comprehensive behavioral weight loss therapies focusing on sleep behavior as well as physical activity and eating behaviors. In addition to the absolute amounts of physical activity, energy intake, and sleep, emerging evidence suggests that temporal patterns (timing across the 24h day and consistency day-to-day) of these behaviors influence weight loss outcomes. The global hypothesis is of this application is that earlier timing of these behaviors (e.g. morning physical activity, eating more calories earlier in the day, earlier bed/ early rise times) and consistency (day-to-day and weekday-to-weekend) will be associated with greater weight loss, better adherence to the diet and physical activity prescriptions during a behavioral weight loss intervention, and weight loss maintenance. Identifying temporal patterns of these behaviors that are associated with enhanced adherence and greater weight loss will aid in the development of novel, translatable, and effective behavioral strategies for long-term weight loss. The proposed research plan will advance the career of the applicant, Seth A. Creasy, PhD facilitating his transition to independent investigator status over the five years of K01 support. A team of highly productive, multidisciplinary scientists (Drs. Edward Melanson, Victoria Catenacci, Nichole Carlson, Celine Vetter, Valerie Myers) will collectively serve as mentors to Dr. Creasy during the proposed research at the University of Colorado ? Anschutz Medical Campus. This team of mentors has the expertise to train Dr. Creasy in physical activity assessment methods, doubly labeled water theory and methodology, assessing energy intake, novel metrics for quantifying times-series data, and developing/conducting large, clinical weight loss interventions. In sum, the proposed training and expert mentoring team will provide Dr. Creasy with the skillset and preliminary data necessary to compete for R01 funding, and this award will serve as a catalyst making Dr. Creasy a leader in the field of lifestyle interventions for treating and preventing obesity.